targeted-toxins

Bugarith KH, Li A, Dinh TT, Ritter S (2004) Injection of the targeted-toxin, neuropeptide Y-saporin (NPY-SAP), into the basomedial hypothalamus (BMH) disrupts leptin and ghrelin signaling. Neuroscience 2004 Abstracts 893.17. Society for Neuroscience, San Diego, CA.

Summary: NPY-SAP, a conjugate of the peptide NPY and saporin, a ribosomal inactivating toxin, specifically lesions NPY receptor-expressing cells. We injected NPY-SAP into the BMH and examined the effects of various inhibitory (leptin, 5ug/5ul/day, icv; GLP-1, 5ug/5ul, icv, CCK, 4ug/kg, ip;) and stimulatory (ghrelin, 2ug/5ul, icv; NPY, 500ng/100nl, icv; 2-DG, 100, 200 and 400 mg/kg; MA, 68mg/kg, ip) peptide and metabolic signals that influence food intake. We also examined the effect of NPY-SAP on NPY, CART and AGRP mRNA expression in NPY/AGRP and POMC/CART neurons known to express the NPY receptor, and the effect of NPY and NPY Y1 receptor immunoreactivity in the arcuate (Arc) nucleus. We found that the anorectic effects of leptin and the orexigenic effects of ghrelin were abolished by NPY-SAP. The stimulation of feeding induced by NPY, 2-DG and MA, and the suppression of deprivation-induced feeding by GLP-1 and CCK were not attenuated by NPY-SAP injection. There was a profound but localized reduction of NPY Y1 receptor-, and NPY fiber and terminal immunoreactivity, and NPY, AGRP and CART mRNA expression in the Arc. NPY-SAP did not appear to be retrogradely transported in hindbrain NPY neurons with hypothalamic terminals. Leptin and ghrelin are thought to act primarily on Arc NPY/AGRP and POMC/CART neurons to mediate their ingestive effects, whereas the effects of 2-DG, MA, CCK and GLP-1 are thought to be mediated in part by mechanisms outside the Arc. Present results show that BMH injections of NPY-SAP selectively impair controls mediated by Arc neural circuitry without causing widespread disruption of other ingestive behaviors. Results also reveal important ingestive controls that do not require Arc NPY/AGRP and POMC/CART neurons.

Related Products: NPY-SAP (Cat. #IT-28)

Xu W, Zhu JPQ, Angulo JA (2004) Local striatal deletions of neurokinin-1 receptor-expressing neurons protect against methamphetamine-induced neural damage. Neuroscience 2004 Abstracts 908.8. Society for Neuroscience, San Diego, CA.

Summary: Recent collective evidence from our laboratory and others has implicated the peptidergic system involving the neuropeptide substance P (SP) and its receptor, neurokinin-1 (NK-1), in mediating METH-induced adverse effects in the neostriatum. Here we test to see if local striatal abolishment of the NK-1 receptor-signaling pathway can protect from METH-induced neural damage in the striatum. Selective striatal knockouts of this pathway was done using an intrastriatal injection of [Sar9,Met(O2)11]substance P conjugated to the ribosomal-inactivating cytotoxin saporin (SSP-SAP). Selective striatal elimination of NK-1 receptor-expressing neurons demonstrated protection against METH-induced apoptosis by TUNEL-labeling. This further confirms the important modulatory effects of this peptidergic receptor in striatum.

Related Products: SSP-SAP (Cat. #IT-11)

Montoya DA, Pang K (2004) Modulation of late long-term potentiation in the hippocampus: Effect of cholinergic and GABAergic medial septal lesions. Neuroscience 2004 Abstracts 972.12. Society for Neuroscience, San Diego, CA.

Summary: Long Term Potentiation (LTP) is an endurable change in synaptic efficacy produced by brief repetitive stimulation of specific afferents and is a cellular model of long term memory. The duration of LTP can vary depending on the intensity fo the inducing tetanic stimulation, which reflects the different phases of LTP. Early phase LTP does not require protein synthesis, whereas late-phase LTP is dependent on protein synthesis. Modulating transmitter systems may also be important in the conversion of early-phase to late-phase LTP. In previous studies, stimulation of the medial septum (MS) converted an early-phase LTP to a late-phase LTP in the dentate gyrus. These results suggest that cholinergic or GABA septohippocampal neurons may be important in late-phase LTP. The present study will evaluate whether cholinergic or GABAergic septohippocampal neurons are important in the development of long-lasting LTP after MS stimulation. LTP will be assessed in urethane anesthetized rats with prior intraseptal saline, 192 IgG-saporin (SAP; 0.245 micrograms/microliter) or kainic acid KA; 0.5 microgram/microliter) treatment. 192 IgG-saporin selectively destroys cholinergic MS neurons, while kainic acid preferentially damages GABAergic septohippocampal neurons. In preliminary studies, 5 trains of perforant path stimulation (15 pulses at 400 Hz/train) produced a transient LTP of the dentate population spike in urethane anesthetized rats. In this preparation, LTP lasted for about 90 minutes. In future experiments, we will assess whether late-phase LTP develops in the urethane anesthetized rats with MS stimulation followed by perforant path stimulation trains. If this occurs, rats with cholinergic or GABAergic MS lesions will be evaluated.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Gravitt KC, Cai RS, Marson L (2004) Effect of removal of neurons expressing serotonin reuptake transporter on male sexual reflexes. Neuroscience 2004 Abstracts 998.2. Society for Neuroscience, San Diego, CA.

Summary: Ejaculatory reflexes are regulated by spinal circuits that are tonically inhibited or facilitated by specific regions of the brain. Serotonin can facilitate or inhibit sexual responses depending on the site of action and the predominate receptor subtype involved. Sexual function, in particular ejaculation, can be reduced by administration of serotonin reuptake inhibitors (SSRI’s). The urethrogenital (UG) reflex comprises erections, rhythmic contractions of perineal muscles and ejaculation in male rats. We previously demonstrated that a direct pathway from the nucleus paragigantocellularis to the lumbosacral cord is involved in regulating the tonic inhibition of UG reflexes. Neurons in the ventral medulla contain serotonin and removal of serotonin inputs in the spinal cord allow the UG reflex to be exposed. The present study examined the effect of specific lesions of ventral medullary neurons containing the serotonin reuptake transporter (SERT) on sexual reflexes. Anti-SERT-saporin (50-100nl, 1uM) was injected bilaterally into the nPGi of male rats. Ten-fourteen days following surgery, animals were deeply anesthetized and the presence of the UG reflex examined. Urethral stimulation was performed before and after cutting the spinal cord (SCT) and recordings made from the bulbospongiosus muscle. Following the experiment immunocytochemical localization of serotonin was examined. In control rats the UG reflex was not present before SCT. In 50% of males that received anti-SERT-saporin the UG reflex was exposed before SCT. Responses after spinal cord transection were similar in all groups. Rats treated with ant-SERT-saporin showed a significant reduction in the number of serotonin containing neurons and a decrease in the intensity staining in the nPGi, parapyramidal region and medullary raphe. These studies suggest that neurons containing serotonin reuptake transporter systems are involved inhibiting male sexual reflexes.

Related Products: Anti-SERT-SAP (Cat. #IT-23)

Xu F, Zhuang J, Hernandez J, Shi S (2004) Apnea induced by stimulation of bronchopulmonary C-fibers (PCFs) depends on neurons expressing the neurokinin a receptor (NK1R) in the commissural subnucleus of the nucleus tractus solitarius (cNTS). Neuroscience 2004 Abstracts 661.13. Society for Neuroscience, San Diego, CA.

Summary: Stimulation of PCFs by right atrial injection of capsaicin (CAP) reflexly produces an apnea and hypotension via stimulating cNTS neurons. Recent evidence indicates that activation of NK1R within the cNTS significantly amplifies this apneic response (Mutoh, et al., Am J Physiol, 2000). We asked whether the cNTS contained the highest density of the neurons responding to PCF stimulation and expressing NK1R, and what the effect of selective destruction of these neurons was on the cardiorespiratory responses to CAP. In the first series of our experiments, double labeling (c-fos and NK1R immunoreactivity) was used to mark the medullary neurons that were activated by right atrial injection of CAP (0.5-1.0 µg) and displayed NK1R. We found that compared to control (vehicle injection), the greatest enhancement of and highest density of Fos expression were observed within the cNTS, and a number of Fos-stained cNTS neurons had expression of NK1R. In the second series of our experiments, bilateral microinjection (100 nl) of substance P-saporin conjugate (SP-SAP) to selectively destroy the local neurons containing NK1R and SAP (control) into the cNTS was performed in two groups of rats, respectively. Our results showed that at 18 days after SP-SAP (rather than SAP) injection, the majority of cNTS NK1R neurons were destroyed. This lesion did not significantly change cardiorespiratory baseline variables, but did eliminate the apnea and reduce the hypotension induced by CAP. In sharp contrast, the lesion failed to affect the cardiorespiratory responses to hypoxia (10% O2 for 1 min). These findings strongly suggest that cNTS neurons with NK1R are necessary for the PCF-mediated cardiorespiratory responses but are not significantly involved in the cardiorespiratory response to acute hypoxia.

Related Products: SP-SAP (Cat. #IT-07)

Conner JM, Chiba AA, Tuszynski MH (2004) The basal forebrain cholinergic system is essential for cortical plasticity and functional recovery following brain injury. Neuroscience 2004 Abstracts 685.12. Society for Neuroscience, San Diego, CA.

Summary: Localized damage to the motor cortex typically results in impaired motor function. Functional recovery following focal brain injury presumably requires the reorganization of cortical circuitry, enabling undamaged areas remote from the lesion site to take over function. Neuronal mechanisms mediating plasticity of cortical representations are not fully understood, but recent studies have indicated that the basal forebrain cholinergic system may play an essential role. In the present study, we investigated the hypothesis that the basal forebrain cholinergic system is essential for enabling cortical reorganization required for functional recovery following focal motor cortex lesions. Following focal cortical injury, performance in a previously learned skilled reaching task dropped by ~75%. After 5-weeks of rehabilitative training, normal (cholinergically-intact) rats recovered 55.2 ± 4.4% of their pre-lesion reaching performance. Rats with specific lesions of the cholinergic neurons projecting to the cortex showed only 18.1 ± 7.7% recovery (p<0.002). Intracortical mapping revealed that massive reorganization of motor representations had occurred in the cortex following focal cortical injury and rehabilitative training. A significant 48.6 ± 12.2% increase (p=0.001) in the size of the rostral forelimb area (RFA) was seen in cholinergically-intact, functionally recovered, rats. In contrast, the size of the RFA did not change in cholinergic-lesioned animals. Subsequent ablation of the RFA completely disrupted skilled reaching performance, suggesting the RFA was essential to the recovered function. These results demonstrate that functional recovery following discrete cortical injury requires basal forebrain cholinergic mechanisms and suggest that the basis for this recovery is the cholinergic-dependent reorganization of motor representations.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Tait DS, Brown VJ (2004) Cell-body lesions of basal forebrain impair reversal learning but not attentional set-shifting in rats. Neuroscience 2004 Abstracts 779.12. Society for Neuroscience, San Diego, CA.

Summary: There is considerable evidence for a role of basal forebrain acetylcholine in a wide range of attentional tasks (see Sarter & Bruno, 2000, Neurosci, 95:933-952), but previous work from this laboratory found that basal forebrain cholinergic projections are not critical for the acquisition, maintenance and shifting of attentional set (Tait et al, 2002 SfN abstr 286.2). As GABAergic basal forebrain projections to cortex may be important for “cognitive flexibility” (Sarter & Bruno, 2002, Eur J Nsci, 15:1867-1873), the present study assessed the effects of non-specific basal forebrain lesions. Male Lister hooded rats received infusions of 200nl 0.06M ibotenic acid into basal forebrain, at coordinates: nosebar –3.3; AP –0.9; ML ±2.9; DV –6.9. We used the rat attentional-set shifting task (Birrell & Brown, 2000, JNsci, 20:4320-4324), in which rats forage in digging bowls for food rewards, to assess discrimination learning (based on the odor of the bowls or the medium in which the food was hidden), reversal learning and attentional-set shifting (when the relevant aspect of the stimulus is switched; for example, a rat previously attending to odor, now must attend to digging medium or vice versa). There was no impairment in discrimination acquisition or in shifting of attentional-set. Lesioned rats were impaired only on the first of three discrimination reversals, taking significantly longer to reach criterion than controls. Prior evidence indicating no effect of selective BF cholinergic depletion via 192-IgG-saporin administration on reversal performance (Tait et al, 2002) leads us to conclude that the non-cholinergic neurons – most likely the GABAergic projection to prefrontal cortex and thalamus – have an important role in reversal learning. These data are strikingly similar to the effects of excitotoxic basal forebrain lesions in monkeys (Roberts et al, 1992, NSci, 472:251-264).

Related Products: 192-IgG-SAP (Cat. #IT-01)

Cordova CA, Yu AJ, Chiba AA (2004) Attention, uncertainty, and acetylcholine: Effects of nucleus basalis cholinergic lesions on probabilistic inference. Neuroscience 2004 Abstracts 779.13. Society for Neuroscience, San Diego, CA.

Summary: Animal investigations suggest that the basal forebrain corticopetal cholinergic system helps to regulate attention to unpredictable events. In light of these findings, computational theorists propose that cholinergic neurons precisely alter the way that sensory stimuli are processed in the cortex in light of how well predicted they are. In an initial test of this theory, two groups of rats were trained to respond to probabilistic stimuli presented serially in one of four spatial locations with varying degrees of predictive uncertainty (arising from a 2-layer Hidden Markov model). Following training, one group of rats was given a selective cholinergic lesion of the nucleus basalis/substantia innominata region of the basal forebrain using 192-IgG Saporin. The lesioned rats were unable to allocate attention appropriately, as evidenced by the decreased accuracy of responses to less probable stimuli. These findings provide support for the notion that the basal forebrain corticoptetal cholinergic system facilitates attention by regulating the balance of learned expectations and sensory processing during stimulus inference.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Taylor CL, Rostron PR, Latimer MP, Winn P (2004) Behavioral characteristics of pedunculopontine tegmental nucleus lesioned and nucleus basalis magnocellularis lesioned rats in a test of vigilance. Neuroscience 2004 Abstracts 780.4. Society for Neuroscience, San Diego, CA.

Summary: Previous work has shown pedunculopontine tegmental nucleus (PPTg) lesioned rats make more omissions on a vigilance task but improve if the target is longer. We compared vigilance performance of PPTg rats with rats bearing 192 IgG Saporin lesions of the nucleus basalis magnocellularis (NbM). The task involved a period of darkness before a dim light of variable duration, followed by a bright light target. A lever press was required during the target to receive food reward, while failure to press during the target constituted an omission. Rats were pre-trained to a criterion of >70% correct and <20% omissions at 1500ms target duration. Post-lesion, rats were assessed for 10 days at 1500ms, 5 days at 4000ms, and 5 further days at 1500ms target durations. Results showed both groups increased omissions relative to controls but this effect was transient in NbM rats. The percentage of omissions in all groups was sensitive to manipulation of target duration. Because increasing target duration also increased the time allowed to make a correct response we re-coded omissions in the 1500ms task to include only those occurring a further 2500ms following target offset (making the response time frame comparable with the 4000ms task). Again, comparison with omissions from the 4000ms task continued to show target duration sensitivity. This finding lends support to PPTg as well as NbM involvement in attention. In order to address why lesioned rats made more omissions in the task we analyzed video data of behaviour at the time of the dim and bright light. Results suggest increased distraction in PPTg lesioned rats while NbM lesioned rats additionally showed failed attempts to lever press in response to the bright signal. This finding has implications for studies using short response time frames where NbM rats may not have time to recover from a failed lever press attempt.

Related Products: 192-IgG-SAP (Cat. #IT-01)

Truitt WA, Dietrich AD, Fitz SD, Minick PE, Shekhar A (2004) Neurokinin 1 receptor expressing interneurons of the BLA regulate anxiety-like responses in the rat. Neuroscience 2004 Abstracts 782.5. Society for Neuroscience, San Diego, CA.

Summary: The Basolateral Nucleus of the Amygdala (BLA) has been implicated in the regulation and development of anxiety. In general, regarding BLA projection neurons, excitation tends to increase, while inhibition tends to reduce anxiety-like responses. These projection neurons, which comprise approximately 85% of the BLA neurons, are tightly regulated by the activity of local circuit GABAergic interneurons. To date, at least four distinct interneuronal subpopulations have been identified in the BLA, with characteristic morphological and physiological properties suggestive of functional diversity. Yet the in vivo functional selectivity of these subpopulations has not been critically examined. Here we propose to examine the function of one specific interneuronal subpopulation within the BLA by making selective lesions and monitoring anxiety-like behavior. To accomplish this objective the subpopulation of BLA interneurons expressing NK-1r receptors were ablated with the targeted toxin SSP-saporin (SAP). Lesions were made by a series of 6 bilateral, 500nl injections spread throughout the anterior BLA. Control rats were injected with an equal volume of blank-SAP, which does not enter the cells. SSP-SAP injections significantly reduced the number of NK-1r expressing cells compared to blank-SAP treated rats, with little to no nonspecific damage. Lesioning NK-1r expressing cells resulted in increased anxiety-like responses in the social interaction (SI) and elevated plus maze (EPM) tests. Specifically, SI time compared to pre-surgery value was significantly reduced in lesion rats. Lesion rats also had fewer open arm entries in the EPM compared to control rats. Furthermore, lesioned rats failed to recover from this decrease in SI even after 4 weeks of testing. These results suggest that the subpopulation of interneurons within the BLA that express NK-1r is critical in regulating anxiety-like behavior.

Related Products: SSP-SAP (Cat. #IT-11)